Britannia was ruled by the Celts and was taken over by the Romans. Between Scotland and England a great wall was built by Hadrain. It was called Hadrain's wall. The wall was twelve feet tall and eight feet wide. It keept out barbarians for hundreds of years. Britannia has a natural barrier because of the brutal waves of the English Channel. The wall was not all that good. The Germanic people a.k.a the Barbarians came in. They were given credit for crushing the Roman Empire.